In a vacuum deposition method, a method in which gas introduced in a vacuum chamber is ionized to generate a cation whereby evaporated molecules are pressed against a substrate, thereby forming a thin film which is strong in coherence and dense is generally referred to as Ion Assist Deposition (hereinafter abbreviated as “IAD”).
FIG. 4 shows a schematic diagram of an optical thin-film vacuum-deposition device based on a radio-frequency voltage direct application system using the IAD method. The following outlines the formation of thin film using the system shown in the same figure.
In the vacuum chamber 30 are arranged a deposition substrate 23, substrate dome 22 on which the deposition substrate 23 is mounted, substrate dome rotation mechanism 24, substrate heater 33 for heating the deposition substrate 23, deposition material 34, crucible 35 filled with the deposition material, electron gun 36 for heating the deposition material 34 to evaporating temperature, shutter 37 for closing when deposition is completed to shield the deposition material, gas inlet 31 for introducing gas into the vacuum chamber, power supply mechanism 32 for applying radio frequency voltage across the substrate dome 22 being rotating and neutralizer 38 for emitting electrons.
When deposition is performed with the device shown in the same figure, the deposition substrate 23 is first attached to the substrate dome 22 and the crucible 35 is filled with the deposition material 34. Air is evacuated from the vacuum chamber 30 with an exhaust system (not shown), thereafter, the substrate dome 22 is rotated by the substrate dome rotation mechanism 24 and the deposition substrate 23 is heated under the substrate heater 33. At a time when degree of vacuum and temperature of the substrate reach target values, the deposition material 34 is irradiated with electron beams from the electron gun 36 to raise the temperature thereof to evaporating temperature. At the same time, gas is let in the vacuum chamber through the gas inlet 31 and electrons are emitted from the neutralizer 38. Radio frequency voltage is applied across the substrate dome 22 using the power supply mechanism 32 to ionize gas introduced from the gas inlet 31, thereby generating plasma in the vacuum chamber 30. The open of the shutter 37 causes the deposition material 34 to spatter inside the vacuum chamber and to be deposited on the deposition substrate 23 with an assist from ions, thereby forming a dense thin film. At a time when the thickness of film reaches a target value, the shutter 37 is closed, then the electron gun 36, substrate heater 33, power supply mechanism 32, introduction of gas, and neutralizer 38 are stopped. After cooling down, air is introduced into the vacuum chamber and then the deposition substrate 23 on which the thin film is formed may be taken out.
The aforementioned vacuum deposition device is disclosed in, for example, Patent Document 1.
FIG. 5(B) shows a schematic plan view of the power supply mechanism 32 illustrated in FIG. 4. FIG. 5(A) shows a schematic cross section taken along line Z-Z′ in FIG. 5(B). The plan view shown in FIG. 5(B) illustrates the power supply mechanism 32 arranged in the vacuum chamber when viewed from the bottom plate to the top one. FIG. 6 shows a detailed schematic diagram of the power supply mechanism 32 and peripherals thereof. In the following a conventional power supply mechanism 32 is described with reference to FIGS. 5 and 6.
The power supply mechanism 32 is composed of a disk-shaped base 40 to which radio frequency power is supplied through a copper plate 28 from a radio-frequency power supply (not shown) installed outside the vacuum chamber 30, the base being electrically insulated from the vacuum chamber 30, contact 41 being an electrode for contacting a rotating body to supply electric power thereto, contact base 42 for fixing and arranging the contact 41, two pins 43 fixed to and arranged on the base and for holding the contact base, power supply thin plate 44 which assists in supplying radio frequency power from the base 40 to the contact base 42 and two springs 45 arranged between the base 40 and contact base 42. The contact 41, contact base 42, pins 43, springs 45 and power supply thin plate 44 form one contact unit. A plurality of the contact units are arranged on the base 40. For example, four contact units are mounted on one device whose substrate dome is about φ700 to 1200 in diameter.
A rotating body composed of the substrate dome 22, a dome catcher 51, a dome adapter 50 and a power supply plate 52 is electrically insulated from and rotatably arranged inside the vacuum chamber 30 and integrally rotated. The power supply plate 52 is fixed and arranged on the dome adapter 50 and the power supply mechanism 32 is arranged over the power supply plate 52. FIG. 8 schematically shows states of the contact 41 touching the power supply plate 52. The figure shows the power supply plate 52 when viewed from the top plate to the bottom one in the vacuum chamber. Four contact units are arranged and only contact 41 is shown. The power supply plate 52 is disc-shaped and has a concentric-circle hole at the center thereof. The contact 41 of each unit is attached in such a manner that the longitudinal direction thereof is arranged radially from the center of rotation of the power supply plate 52.
The power supply mechanism 32 is arranged on the top plate of the vacuum chamber through a porcelain insulator 27 and is electrically insulated from the vacuum chamber. The contact 41 as an electrode touches the power supply plate 52 to apply radio frequency voltage across the rotating body. Since the rotating body is arranged in the vacuum chamber using an insulator or the like, electric power is supplied to only the rotating body contacting the power supply mechanism. Thus, the application of radio frequency voltage across the substrate dome 22 being the rotating body allows deposition using the IAD method.
The two pins 43 are inserted into two through holes 46 provided in the contact base 42. The contact base 42 and the contact 41 fixed thereto are movably held along the pins 43. The spring 45 is arranged around the periphery of the pin 43 and the elastic force of the spring 45 provides the contact 41 with a force thrusting the power supply plate 52 through the contact base 42. The cross section of the contact 41 is arc, and the arc curved-surface thereof touches the power supply plate 52. The contact 41 is made of materials such as phosphor bronze and copper.
Fixing the contact 41 to the base 40 may destabilize the contact between the contact 41 and the power supply plate 52 when the contact has been worn with rotation, which fails to stably supply radio frequency power to the substrate dome 22, causing discharge failures. The substrate dome 22 is removed each time deposition is completed, so that a slight error is produced in distance between the power supply plate 52 and the base 40 each time the substrate dome 22 is fixed. For this reason, in the conventional power supply mechanism, the pin 43 has been provided perpendicularly to the plane of the power supply plate 52 to hold the contact base 42 movably along the pin 43, thereby allowing the contact 41 to be thrust perpendicularly to the plane of the power supply plate 52.
Patent Document 1: Japanese Patent Application Laid-Open No. 2001-73136
There has been a problem in that the conventional contact is a small in area where it touches the rotating body and comes into linear contact with the power supply plate, which hastens the wear of the contact. This is because the conventional power supply plate has been subjected to tufftride process to harden the surface thereof, increasing the slip resistance of the power supply plate. The wear of the contact comes out of contact with the power supply plate, causing a problem in that arc discharge is generated to significantly scrape off the tip of the contact part. In addition to the above, there has been another problem in that the tufftride process is liable to increase electrical resistance. A high slip resistance roughens the power supply plate due to wear, increasing electrical resistance by use to lower the power supply efficiency.
The conventional contact comes into linear contact with the rotating body in terms of shape, so that the contact area inevitably becomes small and impedance is increased. Furthermore, there is still another problem in that the wear of the contact part varies the contact area, leading to change in impedance between a new and a worn contact.
Furthermore, the conventional contact unit reciprocates along the two pins arranged perpendicularly with respect to the power supply plate being a rotating body, this results in an operational failure. An external force applied to the contact in the conventional mechanism is described with reference to the FIG. 7. The contact 41 is subjected to its own weight and a force f4 equal to a force applied from the contact 41 to the power supply plate 52 by the elastic force of the spring. In addition, the contact 41 is subjected to a force f5 in the rotational direction (i.e., the direction shown by an arrow “c” in the figure) from the power supply plate 52 by the rotation of the substrate dome 22. The contact 41 is subjected to the resultant force f6 composed of the sum of the forces f4 and f5, however, in the conventional mechanism, the resultant force f6 applied to the contact 41 is not coincident in direction with the move of the contact 41 (i.e., the direction of the arrow “d” shown in the figure), this results in an operational failure. In the conventional mechanism, the contact 41 is arranged in such a manner that the longitudinal direction thereof is radially arranged with respect to the center of rotation, so that the force f5 in the direction of rotation is different depending on a position where the contact 41 touches the power supply plate 52. FIG. 8 schematically shows the direction and magnitude of a force applied to each point of the conventional contact 41. Since the force f5 in the direction of rotation (i.e., the direction of the arrow “e” shown in the figure) is proportional to velocity, the magnitude of force varies from the center where velocity is lower (f5′) and to the outer periphery where velocity is higher (f5″), this produces torsion in the contact (shown by the arrow “f” in the figure).
In addition, the small spring is sensitive to heat to tend to lose elasticity, impeding a smooth vertical motion.